Matchbook

Like switch on runtime steroids, for easily creating overloaded functions.

# CoffeeScript
pattern = 'matchbook'

myFunc = pattern (match) ->
  # TODO: interesting example

// ES 6
let pattern = require('matchbook');

let myFunc = pattern(match => {
  // TODO: interesting example
});

// ES 5
var pattern = require('matchbook');

var myFunc = pattern(function(match) {
  // TODO: interesting example
});

Patterns

Valid patterns are:

• "classes" (constructor functions)
  • The built-in functions Number, String, Boolean, Function, and Array are special-cased.
• arbitrary predicates: If(x => x > 0)
• arrays of patterns: [String, Number, Int]
• objects of patterns: { foo: String, bar: Function }
• literal values: 1, null, true, void 0, etc.

Note that the special-cased primitive patterns (like Number and String) only match primitive values (like 123 and foo), not boxed values (like new Number(123) and new String('foo')).

API

Matchbook exports a function, which I'll call pattern.

let pattern = require('matchbook');

Attached to pattern are some other functions:

• pattern.compile(pattern)
  • converts a pattern into a predicate -- a function that tests that pattern on the given value
  • this is not necessary if you're using the pattern function directly, but can be useful in other cases
• pattern.Any
  • a pattern that matches any value, including undefined
• pattern.If(predicate)
  • returns a predicate-based function
• pattern.List(pattern)
  • returns a pattern that matches on iterators (such as Arrays, and generators) only if each element matches the supplied pattern
• pattern.Or(pattern1, pattern2)
  • returns a pattern that succeeds if either supplied pattern matches
• pattern.And(pattern1, pattern2)
  • returns a pattern that matches if both supplied patterns match
  • example: And(Number, If(x => x > 0))
• pattern.overload
  • a synonym for pattern, for more convenient destructuring imports.

Extracting values from patterns

This is not supported, and cannot be implemented in vanilla JavaScript without some horrible abuse of eval. If it's an option for you, consider a SweetJS-based pattern matcher like Sparkler instead.

Default values, spreads, and views

There is no support yet for default values of functions, nor for spreads, nor for views. But these would not be hard to add, and I'd be happy to do so if there's interest. Or I'll just go ahead and do it if I encounter a need myself.

Compatibility

Matchbook will not work in IE 8 or below.

Changelog

License